19. In cohort 1, must have EGFR S492R or other ectodomain mutation detected from circulating tumor DNA from plasma collected after progression to prior cetuximab. May have a concomitant mutation in KRAS, NRAS, or BRAF, if there is at least a 5-fold higher allele frequency of the most prevalent EGFR mutation than the most prevalent KRAS/NRAS/BRAF mutation.